| Box Competitions Ltd | Information & communication | 2020 |
| Box Hill Ventures Ltd | Other services | 2018 |
| Boxcom Network Services Ltd | Construction | 2018 |
| Boxmoor Apartments Leaseholder Ltd | Real estate | 2026 |
| Boxmoor Apartments Limited | Real estate | 2025 |
| Boxrig Ltd | Construction | 2019 |
| BP Master Cleaners Ltd | Administrative & support | 2021 |
| Bprm Ltd | Construction | 2017 |
| BPT Group Ltd. | Other services | 2005 |
| BR Machine Limited | Wholesale & retail | 2019 |
| Braai Ltd | Real estate | 2018 |
| Brabus Cost Consultants Limited | Professional & scientific | 2010 |
| Brackley & Stone Ltd | Construction | 2022 |
| Bradan Mccallum Limited | Professional & scientific | 2013 |
| Bradway Properties Ltd | Real estate | 2022 |
| Braefoot Associates Ltd | Professional & scientific | 2014 |
| Braemar Residents Co. Limited | Real estate | 1986 |
| Brainsbuddy AI Labs Limited | Wholesale & retail | 2026 |
| Bralas Limited | Real estate | 2020 |
| Brampton Bricks Ltd | Real estate | 2025 |
| Brampton Consultancy Services Ltd | Professional & scientific | 2024 |
| Brand House Holding Ltd | Information & communication | 2017 |
| Brand International Group Limited | Wholesale & retail | 1994 |
| Brand Select (UK) Limited | Wholesale & retail | 2011 |
| Brandbition Ltd | Other services | 2018 |
| Branded Bricks Ltd | Real estate | 2020 |
| Brandface Media Limited | Professional & scientific | 2025 |
| Brandills Consultancy Ltd | Information & communication | 2010 |
| Brandpax Limited | Administrative & support | 2015 |
| Brands of Watford Limited | Wholesale & retail | 2010 |
| Brandsby Project Services Limited | Professional & scientific | 2023 |
| Branston Close Management Company Limited | Households | 2011 |
| Branton BI Services Ltd | Information & communication | 2026 |
| Brar Homes (London) Limited | Real estate | 2026 |
| Brass Master Limited | Manufacturing | 2005 |
| Bravo Management (Watford) Limited | Administrative & support | 2014 |
| Brazil Property Sale Limited | Information & communication | 2017 |
| Brazos Ltd | Wholesale & retail | 2021 |
| Brazuca Bar Watford Ltd | Hospitality | 2023 |
| Brazuca Delivery Limited | Transport & logistics | 2025 |
| BRC Wealth Ltd | Financial services | 2025 |
| BRE Certification | Professional & scientific | 1998 |
| BRE Global Limited | Professional & scientific | 2014 |
| BRE Group Limited | Professional & scientific | 1992 |
| BRE International Limited | Professional & scientific | 1985 |
| BRE Trust | Professional & scientific | 1996 |
| Bread Without Asking Ltd | Wholesale & retail | 2023 |
| Breakshot Games Limited | Information & communication | 2020 |
| Breakspear Place Limited | Households | 2005 |
| Breakup.Biz Limited | Arts & recreation | 2009 |
| Brealy Management Company (NO. 3) Limited | Households | 1987 |
| Breaux Bridge Ltd | Information & communication | 2017 |
| Bredbury Computing Ltd | Information & communication | 2017 |
| Breland Development Limited | Information & communication | 2009 |
| Brendaesthetics Limited | Other services | 2019 |
| Brendan Flynn Construction Limited | Construction | 1975 |
| Brendan Flynn Holdings Limited | Financial services | 2011 |
| Brendon Court Management Limited | Households | 1997 |
| Brendon Investments Limited | Real estate | 2017 |
| Brent Property Services Ltd | Construction | 2013 |
| Breslin Ventures LLP | | 2024 |
| Brex Interiors Ltd | Construction | 2018 |
| BRG Power Ltd | Construction | 2025 |
| Brian Dumbleton & Sons Limited | Construction | 1973 |
| Brick Digital Ltd | Professional & scientific | 2018 |
| Bridel Consulting UK Limited | Professional & scientific | 2018 |
| Bridge the GAP Hub CIC | Administrative & support | 2024 |
| Bridgepoint Advisory Ltd | Professional & scientific | 2025 |
| Bridgeway Property Group Ltd | Real estate | 2025 |
| Bridgeway Recruitment Ltd | Administrative & support | 2016 |
| Bridging Warehouse Limited | Financial services | 2017 |
| Bright Bamboo Ltd | Administrative & support | 2019 |
| Bright Electric Services Ltd | Construction | 2021 |
| Bright House Buyers Ltd | Real estate | 2020 |
| Bright Idea Marketing & Signage Ltd | Manufacturing | 2020 |
| Bright Little Stars Watford Limited | Education | 2014 |
| Bright Media Management Limited | Professional & scientific | 2021 |
| Bright Mind Arts Limited | Education | 2024 |
| Bright Pigeon Ltd | Professional & scientific | 2018 |
| Bright Puppies Ltd | Other services | 2024 |
| Bright Spark Electrical Ltd | Construction | 2020 |
| Brighter Living Commercial Ltd | Real estate | 2024 |
| Brighterr Homes Ltd | Health & social care | 2025 |
| Brightman Builders Limited | Construction | 2020 |
| Brightmen & Sons Ltd | Wholesale & retail | 2023 |
| Brightmen Ltd | Financial services | 2012 |
| Brighton Kitchen Management Ltd | Hospitality | 2019 |
| Brightopal Property Management Limited | Real estate | 2003 |
| Brightsplit 1 Limited | Real estate | 1999 |
| Brightsplit 10 Limited | Real estate | 2019 |
| Brightsplit 2 Limited | Real estate | 2004 |
| Brightsplit 3 Limited | Real estate | 2005 |
| Brightsplit 4 Limited | Real estate | 2005 |
| Brightsplit 5 Limited | Real estate | 2019 |
| Brightsplit 6 Limited | Real estate | 2019 |
| Brightsplit 7 Limited | Real estate | 2019 |
| Brightsplit 8 Limited | Real estate | 2019 |
| Brightsplit 9 Limited | Real estate | 2019 |
| Brightsplit Limited | Real estate | 1988 |
| Brightwall Limited | Construction | 2017 |